Safety helmets are well known and in common use, most safety helmets comprising an outer moulding of plastics material in contact with an inner close fitting foam moulding. In case of an accident, the helmet is usually capable of withstanding the shock loads, providing two stages of deceleration, and there is a degree of resilience before the helmet applies force to the head, and even when this occurs, the force is more evenly spread and over a wider area by partial collapse of the foam, so that the danger of concussion is reduced.
One object of this invention is to provide improvements whereby there is still a further stage of deceleration upon impact, so that the danger of concussion is still further reduced.
One objection which is sometimes levelled against safety helmets is their inability to "breathe", and the consequential high degree of heat which is imparted through the helmet to the skull, and sometimes this is in addition to heat generated within the helmet by the head of a user. In order to overcome this problem in the past it has been known to utilise a helmet having a single body with vents therein, but the vents provided only limited effect as far as ventilation is concerned, and further, the existence of vent apertures resulted in loss of some mechanical strength of the helmet.
There is also frequently a requirement of change of style of a helmet, particularly when used for sporting activities, and prior art helmets have not usually provided facilities for such change.